A NAND-type flash memory is known as an electrically rewritable nonvolatile semiconductor storage device capable of achieving high density integration.
A memory cell of a NAND-type flash memory includes at least one of a charge storage layer formed on a semiconductor substrate with a tunnel insulating film interposed therebetween and a control gate laminated thereon with an inter gate insulating film interposed therebetween, and the memory cell stores data with charge storage state of the charge storage layer in a nonvolatile manner.
In recent years, the NAND-type flash memory involves various problems along with progress in the reduction of size of the memory cell array.
For example, one of such problems includes the following issue. During erase verification operation in an erase sequence, a threshold voltage of a memory cell appears to be different from an actual threshold voltage due to inter-cell interference effect.